1. Field of the Invention
The present invention relates generally to electronic signal measurement apparatus, and more particularly to a short-duration analog signal events acquisition and display system wherein the maximum and minimum magnitudes of a varying analog signal are detected by peak and valley detectors and then digitized by an analog-to-digital converter, stored and then read out at a slower rate for display in electronic strip chart format to highlight signal anomalies.
2. Description of the Prior Art
In the automotive repair field, as well as in other fields, it has long been important to have instruments available for observing electrical signals occurring at various points within the numerous electrical circuits and signal paths resident in an automobile. Measurements of parameters such as current, voltage, resistance, signal frequency, etc. enable a repair technician to locate and diagnose the numerous problems that occur in a vehicle. Such parameters are typically measured using available apparatus ranging from simple voltage, current and resistance-measuring meters to sophisticated, computerized electronic diagnostic equipment.
Among the most difficult conditions to measure are the intermittent faults commonly referred to as "glitches", i.e., rapid signal transitions of short duration. Previous measurement systems have either sampled the input analog signals slowly and have thereby ignored rapidly varying signal components, or have sought to detect the rapidly varying components by sampling at a rate higher than the rate of change of the signal. Sampling systems which sample at frequencies higher than the input signal frequency are well known in the art. For example, an oscilloscope which operates under this general principal contains complex and expensive electronics. At lower sampling rates, glitches might not be captured by the oscilloscope; at higher sampling rates, glitches are less likely to be displayed. Furthermore, the extra data derived from the much higher sampling rate, when converted to digital form, requires substantial computational capacity. A major shortcoming of the digital oscilloscope is the loss of data that usually occurs following the analog-to-digital conversion. Glitches occurring on the signal are generally captured by the conversion, but not all captured data is displayed.
Another difficulty with prior art sampling systems is that they use complicated electronics for triggering the capture of short-duration analog signal events. Prior art devices have typically utilized both trigger-level and trigger-delay circuitry. Trigger-level circuitry will allow detection of an event if its voltage potential rises above a certain preset level. Trigger-delay circuitry will delay detection of an event for a preset time period after the trigger-level circuitry has noted an event with a voltage potential above its preset level. While both of these techniques allow very accurate detection in voltage potential and time of occurrence, the information obtained is superfluous if all one really needs to know is that a particular event has occurred during a particular time period.
A further difficulty with prior art sampling systems is that if the prior art sampling system uses a single A/D converter on a multiple input-channel device, the sample rate is reduced by 1/n for n channels, further reducing the likelihood of detecting a glitch.
There is thus a need for a relatively simple means for detecting and indicating the occurrence of glitches in electrical circuits. Furthermore, there is a need for a device that "latches" a glitch and displays its occurrence in one of several selectable histogrammic formats so that the user does not have to carefully watch the indicator to notice the transient occurrence of a glitch.